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Functions of Proteins
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Protection (Antibodies)
Regulation (enzymes, hormones)
Structures (Collegen)
Muscle contraction (Actin and Myosin)
Transportation (hemoglobin, ion channels)

Metabolic Fates of Amino Groups
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Amino acids derived from dietary protein are the source of most Amino groups
Most amino acids are metabolized in the liver
Some of the ammonia generated in this process is recycled and used in a
variety of biosynthetic pathways
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This occurs because there are no significant storage sites for amino acids or
proteins, and the accumulation of nitrogenous compounds is ill tolerated
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Glutamate also deaminated in the kidneys

Factors that make Protein Catabolism an Impractical quick
soruce of energy
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Proteins are more difficult to break apart than complex carbohydrates or lipids
Ammonium ion by-product is toxic to cells
Extensive protein catabolism threatens the homeostasis at the cellular and
systems levels because proteins form the most important structural and
functional components of any cell

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Glucogenic vs Ketogenic
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AA can be classified into 2 categories: Ketogenic or Glucogenic
Glucogenic AA produce pyruvate or Krebs Cycle intermediates (αketoglutarate or oxaloacetate) all which are precursors to glucose via
gluconeogenesis
All AA except Lysine and Leucine are atleast partly glucogenic
They are solely ketogenic producing only Acetyl CoA or
AcetoacetylCoA, neither of which can bring about total glucose
production
Amino acids can be classified as being “glucogenic” or “ketogenic”
based on the type of intermediates that are formed during their
breakdown or catabolism
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The catabolism of ketogenic amino acids produces acetyl CoA or
acetoacetyl CoA
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The carbon skeleton finally has one or more of the following fates:
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Synthesis of glucose
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Synthesis of non-essential amino acids
The carbon skeletons of the 20 standard amino acids (or the amino acids of
proteins) are degraded to one of the following seven products—pyruvate, αketoglutarate, succinyl CoA, fumarate, oxaloacetate, acetyl CoA and
acetoacetate
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Ketone Bodies
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Acetoacetate
Acetone
Beta-hydroxybutyrate

Ketogenesis
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Ketone bodies are produced by a process termed ketogenesis
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Under normal conditions, the brain uses glucose as its source of metabolic
fuel
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Metabolism Summary



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